Mycetic Spore
Mycetic Spores are the Tyranids' equivalent of Drop Pods. They could carry Carnifexes. Just think about that for a second. Deepstriking Carnifexes. That's awesome, right? Apparently Games Workshop didn't think so, because they removed the Mycetic spores from the 6th edition codex (or as it shall henceforth be known, "Nerf and the world Nerfs with you"). It is unknown why GW chose to do this, but it's probably because they're incompetent cocksections.
The ChapterHouse Fiasco
Before 4th edition at the earliest, there was a company called ChapterHouse Studios, who was responsible for making a whole ton of supplementary 40K stuff that GW was too fucking lazy to provide, like conversion kits for Tervigons, shoulder pads for popular but less supported Space Marine Chapters, and these babies. GeeDubs, being the greedy fucktards they are, got jealous that someone was trying to actually make things without having to go to to them for even more wallet milking. To this end, they decided to sue Chapter House for copying things they made.
In a shocking turn of events (shocking in that, bad as GeeDubs is, Chapter House was actually guilty with stuff like "Pre-Heresy Terminators"), Chapter House actually won the lawsuit, as GW was trying to sue for things they never made or depicted in art, and thus owned no rights to.
For a while, they just let sleeping dogs lie, being unable to actually sue for things they never made, and being too lazy to try making their own spore pods. However, 6th edition finally rang the death bell for the pods, removing from the Tyranid Codex. And with it went the ability to actually get Zoanthropes anywhere reliably and the aforementioned Fex-Striking. The final death knell rang later that year, as GeeDubs froze all of CHS' assets and ended the production of these spore pods.